Chapter II: Mineral Processing
7. Economic Aspects of Mineral Processing
Size Reduction
Capital cost and operating costs (mainly electric power) rise rapidly with deceasing particle size. Table 11 indicates the typical energy requirements for reduction of feed (lumps) to the indicated size. Very fine material may be lost, which constitutes a financial loss.
Table 11. Approximate energy requirements for size reduction.
Mineral Selection Factors
On balance, mineral separation processes are relatively inexpensive to run. Conditions are generally mild and equipment tends to require little maintenance. The techniques require dispersing the ground ore in a medium (water, or possibly air). The volume of mineral-medium mixture is usually several times greater than that of the ore alone. Therefore large equipment is required to handle these large volumes. This involves high capital cost. Equipment employing higher forces than gravity (>1 G), such as cyclones and shaking tables are more complex, but may be much smaller. This can lower capital costs. The principal energy type is electricity. In general the greater the separation time required, the greater the operating costs.
Flotation requires the use of expensive reagents and some less costly ones (such as lime), but in higher amounts. Reagent consumption is a significant operating expense. Some reagents are derived from petrochemical sources. These become expensive when the cost of oil is high. The operating cost of collectors is related to particle size. For a given mass of ore, finer particles have greater surface area and require greater amounts of reagents. Cost then is proportional to the inverse of (particle size)2.
Separation processes are not 100% efficient. A tradeoff must be made between competing demands: product grade, recovery and costs. Losses of valuable mineral to tailings is an operating loss. Gangue minerals that remain in the concentrate must also be handled and processed, which increases downstream processing costs. Up to 20-30% of the valuable minerals in a complex ore, requiring separation of many products, may be lost during mineral processing.
